The present invention relates to the field of prototype or low volume part making, and particularly to total profile machining of parts such as from blocks of plastic materials using CNC machines, wherein a substantial majority of the surface area of the part is created by the CNC machining.
With the quickening pace of product design schedules, the fast turn-around production of low quantity or prototype parts for testing new designs has become more and more common. Product designers need to move from the drawing board (or, in today's world, the computer screen) to having an example product in hand within weeks if not days. To meet these rapid schedules, many designers have turned to the field of rapid prototyping, to quickly convert their written design drawings into a physical part specimen. Most common rapid prototyping techniques are additive processes, wherein material is added in layers or voxels in the shape desired of the part. Examples of common rapid prototyping techniques include stereo lithography (SLA for stereo lithography apparatus), selective laser sintering (SLS), fused deposition modeling (FDM), laminated object manufacturing (LOM), inkjet-based systems and three-dimensional printing (3DP).
Many rapid prototyping techniques are expensive, and produce a part which, though to some degree dimensionally accurate even for many complex geometries, does not have the physical attributes desired of the final part. Due to the expense on a per part basis, most rapid prototyping techniques are only used for low-volume runs of a part (such as a quantity of 10 or fewer), and not for mid- or high-volume part runs. Lower cost methods of fabricating single part or low-volume runs, which more accurately reflect the physical attributes of the production-run part, are desired.
Machining has long been used to shape metal, wood, plastic and similar solid materials into parts. Machining involves a subtractive process, wherein a solid block of material is held or fixtured in to the tool, and the block is reamed, drilled, sawed, lathed, cut or similarly shaped by removing material from the block to form the shape desired. Computer Numerical Control (“CNC”) machining has accelerated the machining process and become commonplace in many part-making and machine shops. CNC machining generally requires writing of code to instruct the CNC machine which tools and tool paths are needed for the material removal steps. The process for generating CNC tool paths can be simple or difficult depending upon the complexity of the tool paths. For simple profiles, typically having a rectangular, box-like or cylindrical shape which can be readily held with vices on the CNC machine, CNC machining may be a viable option, either in low-, mid- or high-volume runs.
As part shape profiles and geometries are designed to be more complicated, CNC machining often requires the creation of custom fixtures for holding the part during machining. It is not unusual for the design and fabrication of the custom fixturing to involve more time and expense than the design and fabrication of a single part itself. With the added time and complexity associated with custom fixturing, CNC machining is rarely used for low-volumes of parts having more complex shapes which need to be fabricated in a quick turn-around time. For parts in mid- or high-volume runs, the design and fabrication of custom fixtures may be warranted, making machining again a viable option depending upon part shape.
Particularly for mid- or high-volume runs, the tooling time required to CNC machine the part can be expensive. CNC mills typically cost hundreds of thousands of dollars, and it is desired to produce as many parts as possible on as few CNC mills as needed. Several companies are involved in a niche market of analyzing part profiles and providing CNC machining instructions which optimize toolpaths to increase the speed of the CNC machining operation. For instance, Celeritive Technologies, Inc. of Cave Creek, Ariz. is marketing a VoluMill software product/system which smooths out toolpaths to increase material removal rates and reduce milling time for parts being milled. For one part, Celeritive advertises a reduction from a 98 second tooling time to a 50 second tooling time. A 48 second improvement in machining time is not significant if performed on a single or a handful of parts, but can be significant if performed on thousands or millions of parts.
In the VoluMill software product/system, a client-side software program is installed on the customer's computer in conjunction with the customer's CAD/CAM package. The client-side software extracts and bundles geometry and parameter information, which is transmitted to a server-side program. The server-side program calculates the CNC toolpaths and transmits such toolpaths back to the customer's computer. The toolpaths, however, are only to cut pockets, steps, slots, channels, and other prismatic shapes into separately and conventionally fixtured materials.
Conventional fixturing methods for CNC often utilize vises, clamps, vacuum surfaces, and so on. These approaches can obstruct tool access to a significant amount of the part or require difficult repositioning of the part for multiple machining operations. Other fixturing methods utilize sacrificial fixtures or tabbed designs which must be cut by the user after removal from the CNC Mill. Relatively few fixturing methods are available which enable “total profile” machining, i.e., machining a substantial majority of the surface area of the part in the CNC machine. Even with custom fixturing, if the machining time for the part takes too long, often other methods of part manufacture will be more cost effective than “total profile” machining.
Injection molding, among other types of molding techniques, is commonly utilized to produce plastic parts from molds. Once the injection mold is created and the injection mold press is properly set up, injection molding can quickly create parts of complex geometries in quick succession to reach high-volume runs. The work of companies such as the Protomold Division of Proto Labs, Inc. of Maple Plain, Minn. (“Protomold”) has applied CNC machining and computer analysis techniques to moldmaking, and can make injection molds and injection molded parts in an impressive turn-around time for many plastic parts required in low (for instance, 10 or fewer parts) or mid-range (10 to 10,000 parts) volumes. If warranted by volume needs, more elaborate injection molds (typically of tool steel) can be fabricated for higher volumes of injection molded parts, generally with a greater lead time. Because injection molded parts from Protomold are formed of the identical material and by the same technique (injection molding) which would commonly be used for high-volume production runs, such parts are often superior to rapid prototyped parts.
While injection molded parts from Protomold can be achieved at a much lower cost than previously, the cost of one or two parts still requires creation of the injection mold and its associated cost. In cases where only one or several units of a part are required, further cost reductions would be beneficial. Proto Labs, Inc. started its First Cut Prototype Division to address such needs. First Cut Prototype translates the customer's 3D CAD design into instructions for high speed CNC milling equipment, which then total profile machines the parts directly out of blocks of material. Methods of performing such total profile machining are described in U.S. patent Ser. No. 11/586,223, incorporated by reference. Small quantities (1-10) of functional total profile machined parts are typically shipped within one to three days following receipt of the customer's CAD file.
Even the fast speed, low cost processing provided by First Cut Prototype may not be sufficient for some customers. Extremely fast turn around times may be required for certain parts, which simply cannot await for the shipping time to get the parts from First Cut's machining locations to the customer's address. Even faster methods are needed.